A mass data storage library typically stores thousands of data storage media. When the library is powered up, an inventory must be conducted to determine the specific data storage media, if any, stored in each storage shelf.
Typically, the inventory is conducted by a robot in the library. The robot normally is used to transport data storage media between the storage shelves and data storage drives for reading and/or writing data on the media. Hence, instead of transporting media, a scanner, viewer or other sensor mounted on the robot is moved to each individual storage shelf, and is operated to read an identifier on the data storage media stored in the storage shelf, or to detect that the storage shelf is empty. U.S. Pat. No. 5,059,772, Younglove, illustrates an example of an automated magnetic tape cartridge library and a method for taking a library inventory, necessitated by possible manual removal or insertion of cartridges after opening of a library door.
Additionally, a mass data storage library is often employed to store data for a plurality of host computer systems. As the result, each host needs to have an inventory of the storage shelves storing data storage media assigned, either on a sole or on a shared basis, to the host. For example, U.S. Pat. No. 5,416,914, Korngiebel et al., illustrates a single mass data storage library for storing a plurality of types of media, and having a corresponding plurality of types of data storage drives for reading and/or writing on the media. The library is partitioned into corresponding subsets which have consistent mechanical and electrical characteristics, and a management system maps the media type as part of the inventory.
Thus, when the library is powered up, the library must conduct an inventory, and then each host, upon sensing that the library is powered up, will also request an inventory. In prior libraries, each inventory is then separately conducted.
During each of these inventory processes, the library is prevented from transporting any media for two reasons. First, the robot is conducting the inventory and is unavailable, and, second, any movement of a media to or from one storage shelf, or from one storage shelf to another, will corrupt any inventory.
After the inventory is completed, an inventory manager of the library will typically track all movements of the robot and thereby track any changes in position of the media. Thus, the inventory is continually updated.
However, mass data storage libraries often are provided with doors or other access to the storage shelves and/or to the robot. This will allow an operator to repair or modify the robot, or to add or remove media from the storage shelves. Hence, when an access door is opened, the potential exists to modify the content of the library, and the inventory must be again be taken. Therefore, the library is once again removed from service, and the robot operated to take an inventory. Additionally, the hosts may be informed of the access door opening and each will command that an inventory be taken, again prolonging the library's removal from service in order to repeat the inventory.